Reinforcement structure of truss bridge or arch bridge

ABSTRACT

Through co-action between auxiliary triangular structural frames which are each constructed at opposite ends of a truss girder or arch girder and a cable stretched between the auxiliary triangular structural frames, an upward directing force is exerted to the truss girder or arch girder, thereby effectively inducing a load resisting force. A reinforcement structure of a truss bridge or arch bridge is comprised of a truss girder  2  or arch girder a first and a second end of which are each provided with a main triangular structural frame  6  which is further provided at an inner side thereof with an auxiliary triangular structural frame  9,  the auxiliary triangular structural frame  9  being joined at vertexes thereof with frame structural elements at the respective sides of the main triangular structural frame  6,  a cable  10  extending in a longitudinal direction of the truss bridge being stretched between a nearby part of the joined part at the vertex of the auxiliary triangular structural frame  9  on the side of the first end of the truss girder  2  or arch girder and a nearby part of the joined part at the corresponding vertex of the auxiliary triangular structural frame  9  on the side of the second end of the truss girder  2  or arch girder, deflecting means  11  adapted to exert a downward directing force to the cable  10  being inserted between the cable  10  and a lower chord  3  of the truss girder  2  or arch girder so as to tension the cable  10,  an upward directing force being exerted to the lower chord  3  by a reacting force attributable to tension of the cable  10  through the deflecting means  11.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a reinforcement structure effective for improving a load resisting force of a truss bridge or arch bridge constructed over a river or on the land.

[0003] 2. Related Art

[0004] There has heretofore been known, as a work for reinforcing a truss bridge or arch bridge, a method in which a structural frame(s) of a truss girder or arch girder which constitutes the truss bridge or arch bridge, more specifically, an upper chord, a lower chord and a diagonal member in the truss girder or a lower chord and a vertical member in the arch girder are abutted and overlaid by a short reinforcement member and bolted together, so that the sectional area of each structural frame is increased to thereby enhance the load resisting force.

[0005] However, the above-mentioned reinforcement work requires such a troublesome work that many reinforcement plates are needed and each sheet must be bolted. In addition, a long period of time is required for the work and the working cost is increased.

[0006] Moreover, many bolt heads are projected from the joined part of the structural frame through a gusset plate. In case the reinforcement plates are overlaid on the area of the structural frame which excludes this joined part, a problem arises in which the load resisting force is hardly enhanced at the joined part on which a dead load and an active load are concentrated.

[0007] In order to avoid this problem, a large-scale work is required in which many bolts and gusset plates are removed from the joined part and replaced with a reinforcement plate and then bolted again.

SUMMARY OF THE INVENTION

[0008] It is, therefore, an object of the present invention to provide a reinforcement structure of a truss bridge or arch bridge, in which through co-action between auxiliary triangular structural frames which are each constructed at opposite ends of a truss girder or arch girder and a cable stretched between the auxiliary triangular structural frames, an upward directing force is exerted to the truss girder or arch girder, thereby effectively inducing a load resisting force.

[0009] To achieve the above object, from one aspect of the present invention, there is provided a reinforcement structure of a truss bridge comprising a truss girder a first and a second end of which are each provided with a main triangular structural frame which is further provided at an inner side thereof with an auxiliary triangular structural frame, the auxiliary triangular structural frame being joined at vertexes thereof with frame structural elements at the respective sides of the main triangular structural frame, a cable extending in a longitudinal direction of the truss bridge being stretched between a nearby part of the joined part at the vertex of the auxiliary triangular structural frame on the side of the first end of the truss girder and a nearby part of the joined part at the corresponding vertex of the auxiliary triangular structural frame on the side of the second end of the truss girder, deflecting means adapted to exert a downward directing force to the cable being inserted between the cable and a lower chord of the truss girder so as to tension the cable, an upward directing force being exerted to the lower chord by a reacting force attributable to tension of the cable through the deflecting means.

[0010] From another aspect of the invention, there is provided a reinforcement structure of an arch bridge comprising an arch girder a first and a second end of which are each provided with a main triangular structural frame or main rectangular structural frame which is further provided at an inner side thereof with an auxiliary triangular structural frame, the auxiliary triangular structural frame being joined at vertexes thereof with frame structural elements at the respective sides of the main triangular structural frame or main rectangular structural frame, a cable extending in a longitudinal direction of the arch bridge being stretched between a nearby part of the joined part at the vertex of the auxiliary triangular structural frame on the side of the first end of the arch girder and a nearby part of the joined part at the corresponding vertex of the auxiliary triangular structural frame on the side of the second end of the arch girder, deflecting means adapted to exert a downward directing force to the cable being inserted between the cable and a lower chord of the arch girder so as to tension the cable, an upward directing force being exerted to the lower chord by a reacting force attributable to tension of the cable through the deflecting means.

[0011] Preferably, the deflecting means is constituted by a jack capable of controlling the downward directing force by controlling an expanding/contracting amount.

BRIEF DESCRIPTION OF THE DRAWING

[0012]FIG. 1 is a side view schematically showing a reinforcement structure of a truss girder.

[0013]FIG. 2(A) is an enlarged side view of the reinforcement structural part of FIG. 1 and FIG. 2(B) is an enlarged side view of an anchor part of a cable.

[0014]FIG. 3 is a side view schematically showing another example of a reinforcement structure of a truss girder.

[0015]FIG. 4 is an enlarged side view of the reinforcement structural part of FIG. 3.

[0016]FIG. 5 is a side view schematically showing a reinforcement structure of a truss bridge having such a structure that a floor plate is loaded on the truss girder.

[0017]FIG. 6 is a sectional view, when viewed in a widthwise direction of the bridge, showing a part provided with deflecting means in the truss girder of FIGS. 1 through 4.

[0018]FIG. 7 is a side view showing an axial force in each part of the reinforcement structure of FIGS. 1 and 2.

[0019]FIG. 8 is a side view schematically showing a reinforcement structure of an arch girder.

[0020]FIG. 9 is a side view schematically showing another example of a reinforcement structure of an arch girder.

[0021]FIG. 10 is a side view schematically showing a further example of a reinforcement structure of an arch girder.

[0022] FIGS. 11(A) and 11(B) are sectional views showing an operating state of a jack forming deflecting means.

[0023]FIG. 12 is a side view of a reinforcement structure of a truss bridge showing a comparative example of the present invention.

[0024]FIG. 13 is a side view showing another comparative example of the above.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Embodiments of a reinforcement structure of a truss bridge or arch bridge according to the present invention will be described hereinafter with reference to FIGS. 1 through 11.

[0026] As shown in FIGS. 1 through 7, a truss bridge is a bridge having two truss girders 2 each of which is constructed on each side in a sense of a road width direction of a floor slab 1. The truss girder 2 has a structure in which a lower chord 3 and an upper chord 4 are joined by a plurality of diagonal members 5 which are inserted therebetween in a zigzag manner, thereby forming a plurality of main triangular frames 6 from one of the truss girder 2 to the other end.

[0027] On the other hand, as shown in FIGS. 8 through 10, an arch bridge is a bridge having two arch girders 7 each of which is constructed on each side in a sense of a road width direction of a floor slab 1. The arch bridge has a structure in which a lower chord 3 and an arch member 4′ are joined by a plurality of vertical members 8 inserted therebetween in parallel relation, thereby forming a plurality of rectangular structural frames 6′ between two main triangular structural frames 5 each of which is formed on each end of the arch bridge.

[0028] The truss girders 2 and the arch girders 7, as well as other vertical girders 22, are supported, in a suspending manner, at opposite ends thereof on bridge legs 24.

[0029] The reinforcement structure of the truss bridge will be described first. FIGS. 1 through 4 show an example in which a truss girder 2 is arranged such that an upper chord 4 is located above a floor slab 1, and FIG. 5 shows a truss bridge in which a floor slab 1 is loaded on a truss girder 2. The description to follow is common to those two truss girders.

[0030] As shown in FIGS. 1 through 7, a first and a second end of the truss girder 2 are each provided with a main triangular structural frame 6 which is further provided at an inner side thereof with an auxiliary triangular structural frame 9, and the auxiliary triangular structural frame 9 is joined at vertexes thereof with frame structural elements at the respective sides of the main triangular structural frame 6. Therefore, each auxiliary triangular structural frame 9 includes joined parts P1, P2 and P3 which correspond to the respective vertexes of a triangle.

[0031] It is most effective to construct the auxiliary triangular structural frame 9 inside the main triangular structural frame 6 which is formed at each end of the truss bridge. However, it may also be constructed inside the main triangular structural frame 6 which is formed at an inner side of the main triangular structural frame 6 which is formed at each end of the truss bridge. That is, the auxiliary triangular structural frames 9 are each mounted on the first and second end side of the truss bridge.

[0032] The main triangular structural frame 6 comprises three main structural frame elements 6 a, 6 b 6 c. The main structural frame element 6 a comprises a lower chord 3 part, the main structural frame elements 6 b, 6 c comprise two diagonal members 5 which are adapted to interconnect the opposite ends of the main structural frame element 6 a and the upper chord 4. The main structural frame elements 6 a, 6 b, 6 c form the respective sides of the triangle.

[0033] On the other hand, the auxiliary triangular structural frame 9 comprises three auxiliary structural frame elements 9 a, 9 b, 9 c. The auxiliary structural frame element 9 a comprises a diagonal member for joining an intermediate part of the main structural frame element 6 b (one diagonal member 5) and an intermediate part of the main structural frame element 6 a, the auxiliary structural frame element 9 b comprises a diagonal member for joining an intermediate part of the main structural frame element 6 c (the other diagonal member 5) and an intermediate part of the main structural frame element 6 a. The auxiliary structural frame element 9 c comprises a chord for joining an intermediate part of the main structural element 6 b as the diagonal member 5 and an intermediate part of the main structural frame element 6 c as the diagonal member 5.

[0034] Accordingly, the auxiliary structural frame elements 9 a, 9 b of the auxiliary triangular structural frame 9 are bolted to the intermediate part of the main structural frame element 6 a through a gusset plate 12 a, the auxiliary structural frame elements 9 a, 9 c are bolted to the intermediate part of the main structural frame element 6 b through a gusset plate 12 b, and the auxiliary structural frame elements 9 b, 9 c are bolted to the intermediate part of the main structural frame element 6 c through a gusset plate 12 c, thereby forming the joined parts P1, P2, P3.

[0035] A cable 10 extending in the longitudinal direction of the bridge is stretched between a nearby area of the joined part at the vertex of the auxiliary triangular structural frame 9 which is located on the first side and a nearby area of the joined part corresponding vertex of the auxiliary triangular structural frame 9 which is located on the second side. Deflecting means 11 for exerting a downward directing force to the cable 10 is inserted between the cable 10 and the lower chord 3 of the truss girder 2, so that an upward directing force W1 caused by reacting force attributable to tension of the cable 10 is exerted to the lower chord 3 through the deflecting means 11.

[0036] The deflecting means 11 is attached to the lower chord 3 by a bolt or the like such that the deflecting means 11 is projected downward with its lower end supporting the cable 10.

[0037] As one preferable example, as shown in FIGS. 1 and 2, the cable 10 extending in the longitudinal direction of the bridge is stretched between the joined parts P1, P2 at the vertexes of the auxiliary triangular structural frames 9 with respect to the lower chord 3, i.e., between the joined parts P1, P2 of the main structural frame elements 6a with respect to the auxiliary structural frame elements 9 a, 9 b, on the first and second end sides. Deflecting means 11 for exerting a downward directing force to the cable 10 is inserted for tensioning the cable 10 between the cable 10 and the lower chord 3 of the truss girder 2, so that an upward directing force W1 is exerted to the lower chord 3 through the deflecting means 11 and an upward directing force W1 is exerted to the bridge through the lower chord 3, while exerting a tensile force to the joined parts P1, P1, by the reacting force attributable to tension of the cable 10.

[0038] As another preferable example, as shown in FIGS. 3 and 4, a cable 10 extending in the longitudinal direction of the bridge is stretched between the joined parts P3, P3 at the vertexes of the auxiliary triangular frames 9 with respect to the main structural frame elements 6 c, i.e., between the joined parts P3, P3 of the main structural frame elements 6 c with respect to the auxiliary structural frame elements 9 b, 9 c, on the first and second end sides. Deflecting means 11 for exerting a downward directing force to the cable 10 is inserted for tensioning the cable 10 between the cable 10 and the lower chord 3 of the truss girder 2, so that an upward directing force W1 is exerted to the lower chord 3 through the deflecting means 11 and an upward directing force W1 is exerted to the bridge through the lower chord 3, while exerting a tensile force to the joined parts P3, P3, by the reacting force attributable to tension of the cable 10.

[0039] Similarly, in the arch bridge, as shown in FIGS. 8 and 9, a first and a second end of an arch girder 7 are each provided with a main triangular structural frame 6 or, as shown in FIG. 10, a main rectangular structural frame 6′, which is further provided at an inner side thereof with an auxiliary triangular structural frame 9. The auxiliary triangular structural frame 9 is joined at vertexes thereof with frame structural elements at the respective sides of the main triangular structural frame 6 or main rectangular structural frame 6′. Therefore, each auxiliary rectangular structural frame 9 includes three joined parts P1, P2, P3 which correspond to the vertexes of a triangle.

[0040] In the same manner as described above, the main triangular structural frames 6 on the first and second ends of the arch girder 7 each comprise three main structural frame elements 6 a, 6 b, 6 c. The main structural frame element 6 a comprises an end part (first or second end part) of the lower chord 3, the main structural frame element 6 b comprises an end part (first or second end part) of the arch member 4′, and the main structural frame element 6 c comprises a vertical member 8 on an end (first end or second end) of the lower chord 3. The main structural frame elements 6 a, 6 b, 6 c form the respective sides of a triangle.

[0041] On the other hand, the auxiliary triangular structural frame 9 comprises three auxiliary structural frame elements 9 a, 9 b, 9 c. The auxiliary structural frame element 9 a comprises a diagonal member for joining an intermediate part of the main structural frame element 6 b (first or second end part of the arch member 4′) and an intermediate part of the main structural frame element 6 a (first or second end part of the lower chord 3), the auxiliary structural frame element 9 b comprises a diagonal member for joining an intermediate part of the main structural frame element 6c (the vertical member 8) and an intermediate part of the main structural frame element 6 a (first or second end part of the lower chord 3). The auxiliary structural frame element 9 c comprises a chord for joining an intermediate part of the main structural element 6 b as the first or second end part of the arch member 4′ and an intermediate part of the main structural frame element 6 c as the vertical member 8.

[0042] Accordingly, the auxiliary structural frame elements 9 a, 9 b of the auxiliary triangular structural frame 9 are bolted to the intermediate part of the main structural frame element 6 a through a gusset plate 12 a, the auxiliary structural frame elements 9 a, 9 c are bolted to the intermediate part of the main structural frame element 6 b through a gusset plate 12 b, and the auxiliary structural frame elements 9 b, 9 c are bolted to the intermediate part of the main structural frame element 6 c through a gusset plate 12 c, thereby forming the joined parts P1, P2, P3.

[0043] As shown in FIG. 10, the main rectangular structural frames 6′ located between the main triangular structural frames 6, 6 on the first and second ends of the arch girder 7 each comprise four main structural frame elements 6 a, 6 b, 6 c, 6 d. The main structural frame element 6 a comprises a lower chord 3 part, the main structural frame elements 6 b, 6 c comprise two vertical members 8 which are adjacent to each other in parallel relation, and the main structural frame element 6 d comprises an arch member 4′ part. The main structural frame elements 6 a, 6 b, 6 c, 6 d form the respective sides of a rectangular.

[0044] On the other hand, the auxiliary triangular structural frame 9 comprises three auxiliary structural frame elements 9 a, 9 b, 9 c. The auxiliary structural frame element 9 a comprises a diagonal member for joining an intermediate part of the main structural frame element 6 b (one vertical member 8) and an intermediate part of the main structural frame element 6 a (the lower chord 3 part), the auxiliary structural frame element 9 b comprises a diagonal member for joining an intermediate part of the main structural frame element 6 c (the other vertical member 8) and an intermediate part of the main structural frame element 6 a (the lower chord 3 part). The auxiliary structural frame element 9 c comprises a chord for joining an intermediate part of the main structural element 6 b as the vertical member 8 and an intermediate part of the main structural frame element 6 c as the vertical member 8.

[0045] Accordingly, the auxiliary structural frame elements 9 a, 9 b of the auxiliary triangular structural frame 9 are bolted to the intermediate part of the main structural frame element 6 a through a gusset plate 12 a, the auxiliary structural frame elements 9 a, 9 c are bolted to the intermediate part of the main structural frame element 6 b through a gusset plate 12 b, and the auxiliary structural frame elements 9 b, 9 c are bolted to the intermediate part of the main structural frame element 6 c through a gusset plate 12 c, thereby forming the joined parts P1, P2, P3.

[0046] In FIG. 10, a pair of auxiliary triangular structural frames 9, 9′ which commonly have the auxiliary structure frame element 9 c as the chord, the auxiliary structural frame elements 9 a′, 9 b′ which comprise the diagonal member of the auxiliary triangular frame 9′ are joined to an intermediate part of the main structural frame 6 d which comprises the arch member 4′ part through the gusset plate 12 d, thereby forming the joined parts P1, P2, P3, P4.

[0047] In other words, a parallelogrammic structural frame, which comprises the auxiliary structural frame elements 9 a, 9 b, 9 a′, 9 b′, is constructed at an inner side of the main rectangular structural frame 6′. A diagonal member comprising the auxiliary structural frame element 9 c is inserted along a diagonal line which joins the opposing vertexes of the parallelogrammic structural frame, and the respective vertexes of the parallelogrammic structural frame are joined to intermediate parts of the main structural frame members 6 a, 6 b, 6 c, 6 d.

[0048] In the arch bridge, a cable 10 extending in a longitudinal direction of the arch bridge is stretched between a nearby part of the joined part at the vertex of the auxiliary triangular structural frame 9 on the side of the first end of the arch girder and a nearby part of the joined part at the corresponding vertex of the auxiliary triangular structural frame 9 on the side of the second end of the arch girder, deflecting means 11 adapted to exert a downward directing force to the cable 10 is inserted between the cable 10 and the lower chord 3 of the arch girder member 4′ so as to tension the cable 10, and an upward directing force W1 is exerted to the lower chord 3 by a reacting force attributable to tension of the cable 10 through the deflecting means 11.

[0049] The deflecting means 11 is attached to the lower chord 3 by a bolt or the like such that the deflecting means 11 is projected downward with its lower end supporting the cable 10.

[0050] As one preferable example, as shown in FIG. 8, the cable 10 extending in the longitudinal direction of the bridge is stretched between the joined parts P1, P2 of the vertexes of the auxiliary triangular structural frames 9 with respect to the lower chord 3, i.e., between the joined parts P1, P2 of the main structural frame elements 6a with respect to the auxiliary structural frame elements 9 a, 9 b, on the first and second ends. Deflecting means 11 for exerting a downward directing force to the cable 10 is inserted for tensioning the cable 10 between the cable 10 and the lower chord 3, so that an upward directing force W1 is exerted to the lower chord 3 through the deflecting means 11 and an upward directing force W1 is exerted to the lower chord 3, while exerting a tensile force to the joined parts P1, P1, by the reacting force attributable to tension of the cable 10.

[0051] As another preferable example, as shown in FIGS. 9 and 10, a cable 10 extending in the longitudinal direction of the bridge is stretched between the joined parts P3, P3 of the vertexes of the auxiliary triangular frames 9 with respect to the main structural frame elements 6 c, i.e., between the joined parts P3, P3 of the main structural frame elements 6 c with respect to the auxiliary structural frame elements 9 b, 9 c, on the first and second end sides. Deflecting means 11 for exerting a downward directing force to the cable 10 is inserted for tensioning the cable 10 between the cable 10 and the lower chord 3, so that an upward directing force W1 is exerted to the lower chord 3 through the deflecting means 11 and an upward directing force W1 is exerted to the bridge through the lower chord 3, while exerting a tensile force to the joined parts P3, P3, by the reacting force attributable to tension of the cable 10.

[0052] A single of plural deflecting means 11 are provided depending on the supporting interval length of the truss bridge or arch bridge. At that time, the cable 10 in the truss bridge or arch bridge diagonally extends between the joined part P1 and the deflecting means 11 on the first end and between the joined part P3 and the deflecting means 11 on the second end, but it horizontally extends between the deflecting means 11, 11.

[0053] In case the opposite ends of the cable 10 are joined to the connecting points P3, the auxiliary structural frame element 9 c is diagonally oriented on a diagonal axis at the diagonally extending part of the cable 10.

[0054] The cable 10 in the truss bridge or arch bridge used in this embodiment is a steel cable called “PC cable”, in which opposite ends of the cable are provided with male threads 14. As shown in FIGS. 2 and 4, cable threaders 13 are each attached to the joined parts P1, P3, and the opposite ends of the cable 10 are inserted in the cable threaders 13. A nut 15 is threadingly engaged with the male thread part of the cable 10 at the outer end of the cable threader 13, and the nut 15 is abutted with the outer end of the cable threader 13 so that the tensioning state of the cable 10 can be maintained.

[0055] That is, the opposite ends or one end of the cable 10 is pulled by a towing machine to create a tensioning state of the cable 10. In that state, the nut 15 is threadingly advanced and abutted with the outer end of the cable threader 13 to maintain the tensioning state of the cable 10. Accordingly, the nut 15 constitutes a stopper against the tensile force.

[0056] In that tensioning state, the cable 10 is, as shown in FIG. 6, is inserted in a cable guide groove 16 formed in a cable guide at a lower end of the deflecting means 11 and urged hard against the deflecting means 11 and tensioned in a state in which a relatively downward directing force is exerted to the cable 10. As a reacting force of this downward directing force, the upward directing force W1 is generated.

[0057] A simple or plural cables 10 are stretched on one side in the widthwise direction of the bridge. In case plural cables 10 are stretched on the opposite sides, a plurality of the cable guide grooves 16 are formed in parallel.

[0058] The floor slab 1 is supported by a vertical girder 22 which is formed of an H-shaped steel extending in the longitudinal direction of the bridge and a horizontal girder 23 which is formed of an H-shaped steel for joining the vertical girders 22. The opposite ends of the horizontal girder 23 are joined to the lower chord 3 formed of an H-shaped steel of the truss girder 2 or arch girder 7. The upward directing force W1 is exerted to the vertical girder 22 through the horizontal girder 23, thereby exerting the upward directing force W1 to the entire bridge.

[0059] A prop post formed of steel or the like is used as the deflecting means 11. Preferably, a jack which can be adjusted in the downward directing force by controlling the expanding/contracting amount is used as the deflecting means 11.

[0060] As the jack, a jack having a hydraulic cylinder structure or pneumatic cylinder structure can be used.

[0061] A thread type jack can also be used. Particularly preferably, a hydraulic thread type jack 11, as shown in FIGS. 11A and 11B, may be used which can be expanded/contracted by hydraulic pressure and which can be fixed in expanding or contracting position by threading engagement.

[0062] That is, a jack 11 is used which has both the hydraulic cylinder structure and thread type jack structure. In this jack 11, one end of a cylinder rod 17 is slidingly fitted airtight to the inside of the cylinder 18, and a male thread is formed at the outer peripheral surface of the other end part of the cylinder rod 17 which projects from the cylinder 18. A stopper flange 19 is threadingly engaged with the male thread, and a hydraulic pressure feed port 21 for feeding a hydraulic pressure into a hydraulic chamber 20 formed at a lower surface of the cylinder rod 17 at an inner bottom part of the cylinder 18 is provided to the cylinder 18.

[0063] By feeding the hydraulic pressure through the hydraulic pressure feed port 21, the cylinder rod 17 is expanded by a constant expanding amount, thereby exerting a constant tensioning force (downward directing force) to the cable 10.

[0064] Then, the downward directing force exerted to the cable 10 is confirmed by a pressure gauge. In the state in which the downward directing force is exerted to the cable 10, the stopper flange 19 is threadingly retracted along the cylinder rod 17 and sat on an end face of the cylinder 18. Hence, contraction of the cylinder rod 17 is prohibited and the expansion is retained so that the downward directing force exerted to the cable 10 is set and retained.

[0065] After the expanding state is retained by prohibiting the threading retraction of cylinder rod 17 by the stopper flange 19, the hydraulic pressure within the hydraulic chamber 20 is extracted through the hydraulic pressure feed port 21. Thereafter, the downward directing pressure exerted to the cable 10 is maintained by the thread type cylinder rod 17, thereby maintaining the tensioning state of the cable 10.

[0066] In case the cable 10 is loosened with the passage of time, the hydraulic pressure is fed again, so that the tensioning state can be corrected and the downward directing force can be corrected.

[0067]FIGS. 12 and 13 show comparison examples of the present invention. That is, as shown in FIG. 12, in case the opposite ends of the cable 10 are stretched between the opposite ends of the truss girder 2 or arch girder 7 without providing the auxiliary triangular structural frame 9 and the deflecting means 11, the tensioning force of the cable 10 merely exerts a main axial force (compressive force), as indicated by arrows, to the lower chord 3, and it is not effectively transmitted to other main structural frames, i.e., the upper chord 4 and the diagonal member 5 in the truss girder 2, or the arch member 4′ and the vertical member 8 in the arch girder 7, thereby reducing the reinforcement effect thereof.

[0068] As shown in FIG. 13, in case the deflecting means 11 is provided between the cable 10 and the lower chord 3 of FIG. 12 and no auxiliary triangular structural frame 9 is provided, an axial force (compressive force and pulling force) as indicated by arrows of FIG. 13 is applied to the main triangular structural frame 6 of the respective girders 2, 7.

[0069] Particularly, in case the auxiliary triangular structural frame 9 is not provided, in the main structural frame 6 a formed by each end part (first or second end part) of the lower chord 3, an axial force as indicated by arrows is applied to the outer main structural frame element part 6 a′ and the inner main structural frame element part 6 a″ with respect to the joined part P1. As a result, a strong shearing force and a bending moment are applied to the joined part P1.

[0070] On the other hand, as shown in FIG. 7, in case the auxiliary triangular structural frame 9 is provided and the cable 10 is stretched between the joined parts P1, P3, no axial force is applied to the outer main structural frame element part 6 a′ with respect to the joined part P1 at all, and no shearing force nor bending moment are applied thereto.

[0071] The tensioning force of the cable 10 is effectively transmitted to other main structural frame, i.e., the upper chord 4 and the diagonal member 5 in the truss girder 2 or the arch member 4′ and the vertical member 8 in the arch girder 7, while exerting an axial force (compressive force) to the lower chord 3, so that the reinforcement effect thereof is effectively induced. Hence, the present invention is suitable as a reinforcement structure of a truss girder 2 or an arch girder 7.

[0072] Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 

What is claimed is:
 1. A reinforcement structure of a truss bridge comprising a truss girder a first and a second end of which are each provided with a main triangular structural frame which is further provided at an inner side thereof with an auxiliary triangular structural frame, said auxiliary triangular structural frame being joined at vertexes thereof with frame structural elements at the respective sides of said main triangular structural frame, a cable extending in a longitudinal direction of said truss bridge being stretched between a nearby part of the joined part at said vertex of said auxiliary triangular structural frame on the side of said first end of said truss girder and a nearby part of the joined part at the corresponding vertex of said auxiliary triangular structural frame on the side of said second end of said truss girder, deflecting means adapted to exert a downward directing force to said cable being inserted between said cable and a lower chord of said truss girder so as to tension said cable, an upward directing force being exerted to said lower chord by a reacting force attributable to tension of said cable through said deflecting means.
 2. A reinforcement structure of an arch bridge comprising an arch girder a first and a second end of which are each provided with a main triangular structural frame or main rectangular structural frame which is further provided at an inner side thereof with an auxiliary triangular structural frame, said auxiliary triangular structural frame being joined at vertexes thereof with frame structural elements at the respective sides of said main triangular structural frame or main rectangular structural frame, a cable extending in a longitudinal direction of said arch bridge being stretched between a nearby part of the joined part at said vertex of said auxiliary triangular structural frame on the side of said first end of said arch girder and a nearby part of the joined part at the corresponding vertex of said auxiliary triangular structural frame on the side of said second end of said arch girder, deflecting means adapted to exert a downward directing force to said cable being inserted between said cable and a lower chord of said arch girder so as to tension said cable, an upward directing force being exerted to said lower chord by a reacting force attributable to tension of said cable through said deflecting means.
 3. A reinforcement structure of a truss bridge or arch bridge according to claim 1 or 2, wherein said deflecting means is constituted by a jack capable of controlling said downward directing force by controlling an expanding/contracting amount. 